1. Field of the Invention
This invention relates to a method for the refrigerated transportation of a product in a hollow-walled container.
2. Description of the Prior Art
Refrigerated transport, also referred to hereinafter by its abbreviation RT, must be available more particularly for maintaining a so-called refrigeration chain for fresh products such as vegetables, fruit, meat or other foods. Sensitive products such as chemicals, biological products and explosives must also be transported in partly refrigerated form. Refrigerated transport (RT) includes refrigeration for trucks, small transporters, railway trucks, containers, ships, and boats, to name just a few.
Known refrigerated transportation essentially uses compressor cooling or refrigeration, a refrigerant being evaporated in the pipes of a refrigerator and cools or refrigerates air or gas (controlled atmosphere).
Heat is removed by producing a cold surface and circulating air or gas being made colder and, once the dew point temperature is reached, is also humidified.
As a function of the heat load, the refrigerator switches on or off or runs in a power-controlled manner. Such mechanical refrigeration systems are expensive and require maintenance, spares, trained mechanics and a complicated and costly power supply in the form of electric, diesel electric or diesel drives, in order to maintain refrigeration in all circumstances.
In certain applications, use is made of indirect cooling or refrigeration for cooling or refrigerating air or gas through the circulation of a refrigerant, e.g. a saline solution through a refrigerator in place of direct evaporation of the refrigerant.
The products are stored in a refrigerated chamber, which is either part of the structure of a motor vehicle or a type of container (hereinafter xe2x80x9cRCxe2x80x9d), which can be loaded and unloaded. Such containers are normally externally insulated to keep heat penetration as low as possible. Containers contain air coolers and devices for circulating air, e.g. fans.
In certain applications, such as e.g. distribution vehicles, the temperature of a container is maintained or changed through the use of so-called eutectic plates, which are conventionally pre-cooled by means of a refrigerator or by placing in a cold storage room. It is also possible to pass air through an ice bed. For special transportation tasks such as e.g. air freight, use is made of CO2. Another practicable way of maintaining or influencing the temperature of containers is to spray N2 into the containers.
Numerous different ways have already been proposed in order to obtain refrigeration for refrigerated transportation and refrigerated containers. Thus, e.g. DE-OS 1 551 365 and EP 664 426 provide for the placing of pipes in the gap between a double wall of a container, and through said gap is pumped a refrigerant (brine), such as e.g. saline solution, which cools a fluid contained in the wall gap, and finally freezes out. Freezing out serves to make available for conversion for a specific time, latent energy (stored frigorific energy), when the refrigerated container is separated from a refrigerator, e.g. during refrigerated transportation periods. The liquid which can be frozen out can be water or a brine, e.g., a saline solution/eutectic.
In practice, in this prior art method, the refrigerated container is connected to a refrigerator and refrigerant is introduced into the pipe system. The cooling process is slow, because the entire structure within the refrigerated container, together with the liquid, must first be cooled and then frozen.
DE-OS 1 751 608 describes a method in which cooling or refrigeration takes place by crushed ice in the wall gaps of a refrigerated container, in order in this way to have an energy storage means during refrigerated transport. This also includes a proposal in which a refrigerated container or the double-walled elements of such a container incorporates a eutectic fluid in a cold chamber prior to refrigerated transport. Reference is also made to DE-OS 2 251 529 which relates to a contact refrigerating or cooling device for the transportation of biological cells and organs, which is pre-cooled by a refrigerator or is cooled by the evaporation of a substance, and which is subsequently cooled with a refrigerator following a certain period of time.
Finally, European Patent Application No. 158 378 proposes a method for compensating the volume expansion of freezing and melting substances in a closed chamber, such as e.g. the refrigerated container double wall.
The problem of the present invention is to provide a system for refrigerated transport, which without great apparatus expenditure rapidly cools the refrigerated container to the temperature corresponding to the intended use, without it being necessary to provide or operate refrigeration units for cooling or during transportation.
According to the invention, this problem is solved by a method having the features of the main claim. The sub-claims contain advantageous embodiments of the invention. The invention makes use of binary ice (BI), which is a suspension of minute ice crystals. Binary ice is produced from an aqueous solution or mixture in special evaporators by cooling a surface and scraping off therefrom the ice crystals produced, or by a direct contact heat exchanger in which the aqueous solution or mixture produces ice crystals in the liquid at the triple point of the liquid (e.g. water 0.1xc2x0 C., 6 mb).
Binary ice is a liquid, pumpable fluid which can also be referred to as slurry ice. Due to the presence of ice crystals in the suspension, the liquid contains latent energy, which significantly increases the enthalpy of the pure liquid, and consequently makes the binary ice an excellent medium for transporting, transferring and storing frigorific energy. In the method according to the present invention, within a very short time there can be a refrigeration or cooling precisely matched to the intended use.
This invention makes use of the unique characteristics of such a binary ice for the dynamic transportation of a refrigeration system. A refrigerated container according to the invention comprises two walls, the outside of which is insulated. The gap contains no pipes and instead merely comprises structural stiffening and baffle plates for the flow and storage of binary ice. Construction is made much easier as a result of the lack of pipes.
Binary ice is made available by a binary ice filling station, which comprises a plurality of binary ice-producing machines and storage tanks for the binary ice and reservoirs for binary ice liquid. Binary ice is produced by different binary ice-producing machines at different temperatures, which are suitable for different cooling or refrigerating uses, e.g. for flowers at +6xc2x0 C., for dairy products at +1xc2x0 C., for fresh fish at xe2x88x921xc2x0 C., for frozen fish at xe2x88x9218xc2x0 C., and for ice cream at xe2x88x9220 C.